A CVD (Chemical Vapor Deposition) method or an ALD (Atomic Layer Deposition) method is known as a method for forming a film on a substrate such as a semiconductor wafer (hereinafter, referred to as “wafer”) or the like. The operations of such a method are performed by accommodating the wafer in a processing chamber in which a vacuum atmosphere is formed and supplying a raw material gas into the processing chamber.
In the case of using a solid raw material, the raw material is sublimated by heating a raw material container in which the raw material is accommodated and, also, a carrier gas is introduced into the raw material container. Then, the raw material gas is supplied into a processing chamber together with the carrier gas.
Such a technique is disadvantageous in that when the remaining amount of the raw material is decreased as the sublimation proceeds, a sublimation flow rate of the raw material is decreased, and when the remaining amount of the raw material is excessively small, the amount of the raw material supplied to the processing chamber becomes unstable. This is considered because a flow velocity of a carrier gas near the surface of the raw material is decreased due to the decrease in the remaining amount of the raw material, and the change in the flow velocity of the carrier gas affects the sublimation of the raw material and the transport amount of the raw material gas by the carrier gas. To that end, conventionally, the raw material container is exchanged with another raw material container filled with the raw material before the remaining amount of the raw material becomes excessively small.
Japanese Patent Application Publication No. H5-291142 discloses a technique for suppressing changes in a vapor pressure of a liquid raw material by mechanically controlling a height position of a liquid surface of the liquid raw material in a container when supplying vapor of the liquid raw material to a reaction furnace. Japanese Patent Application Publication No. 2011-134916 discloses a technique for maintaining a concentration of a raw material gas obtained by sublimating a solid raw material in a tank at a constant level by increasing a set temperature of the tank when a partial pressure of the raw material gas is decreased.
Japanese Patent Application Publication No. 2012-52226 suggests a delivery device including an outlet chamber having a labyrinth for discharging vapor of a solid raw material while suppressing discharge of particles of the solid raw material. In this configuration, the solid raw material is stirred by the carrier gas moving from bottom to top of the delivery device, thereby permitting uniform supply of the vapor of the solid raw material at a high concentration.
The present inventors have studied a technique for stabilizing the sublimation flow rate of the solid raw material regardless of the remaining amount of the raw material, without considerably changing the configuration of the raw material container, when supplying the raw material gas obtained by sublimating the solid raw material together with the carrier gas, and have found that, it is difficult to achieve the above technique by the disclosures of the above-cited references.